Beam-type axle/suspension systems have been used in heavy-duty vehicles such as trucks and tractor-trailers for many years. The heavy-duty vehicle may include more than one beam-type axle/suspension system. Each beam-type axle/suspension system includes a pair of suspension assemblies per axle. The suspension assemblies may be connected with a frame or subframe of the heavy-duty vehicle.
Each suspension assembly of the axle/suspension system includes a hanger that is attached to, and depends from, the frame of the heavy-duty vehicle. Each suspension assembly also includes a longitudinally extending elongated beam. The beam is pivotally mounted at one end portion to the respective hanger. A transversely extending axle has a portion that is attached to the beam at a location spaced from the pivotal end portion of the beam. An end portion of the beam opposite the pivotally mounted end portion is attached to an air spring which is also attached to the frame.
The axle/suspension system provides ride, handling and damping characteristics to the heavy-duty vehicle. More particularly, as the heavy-duty vehicle is traveling over a road, its tires and wheels encounter road conditions that impart various forces, loads, and/or stresses, collectively referred to as “forces”, to the respective axle on which the tires and wheels are mounted. In turn, the forces are transferred to the suspension assemblies that connect with the axle. In order to minimize the detrimental effect of these forces on the heavy-duty vehicle as it is operating, the axle/suspension system is designed to react and to minimize or absorb at least a portion of the forces.
The forces include forces along the vertical direction caused by vertical movement of the tires and wheels as they encounter certain road conditions. The forces also include forces along the horizontal direction due to fore-aft or horizontal movement from acceleration, deceleration and braking of the heavy-duty vehicle. The forces further include lateral and torsional forces associated with transverse vehicle movement, such as turning of the vehicle and lane-change maneuvers. In order to address such various forces, axle/suspension systems have differing design and structural requirements.
For example, it is desirable for an axle/suspension system to be fairly stiff in order to minimize the amount of sway experienced by the heavy-duty vehicle and provide roll stability from lateral forces. It is also desirable for the axle/suspension system to be relatively less stiff or flexible to assist in cushioning the heavy-duty vehicle from vertical forces, while providing compliance so that components of the axle/suspension system are able to withstand the vertical forces. It is further desirable to dampen the vibrations or oscillations that result during operation of the heavy-duty vehicle. A key component of the axle/suspension system that cushions the ride of the heavy-duty vehicle from vertical impacts is the air spring, while a shock absorber typically provides damping characteristics to the axle/suspension system. It is known that air springs may also be designed and constructed to provide damping characteristics.
It is desirable to limit the downward movement of the beams and axle to minimize the possibility of damage to the air spring and/or to other components of the axle/suspension system under certain conditions. For example, when a trailer is lifted onto a railroad car, the beams and axle pivot downwardly. Another example is when the trailer is being backed up and brakes of the heavy-duty vehicle are actuated and cause the axle/suspension system to extend downwardly, called “reverse braking” or, if so equipped, when a slider is repositioned. Also, during operation of the heavy-duty vehicle, the beams and axle may suddenly drop, or move downwardly, as a result of a pothole, or other road hazard. If the downward pivotal movement of the beams and axle is not limited to a predetermined amount, damage to the air spring and/or to other components of the axle/suspension system could result. That is, unabated downward pivotal movement of the beams and axle may overextend the air spring. Limiting downward movement of the beams and axle minimizes the possibility of potential damage to the air spring and/or to other components of the axle/suspension system.
In some heavy-duty vehicles, a chain or pair of chains or shock absorbers are used to limit downward movement of the beams and axle. The chains act as a positive mechanical limiting structure or down-stop. Limiting the downward movement of the beams and axle with the known chains minimizes the possibility of potential damage to the air spring and/or to other components of the axle/suspension system. The chains or other similar mechanical travel limiting devices such as straps, cables, wire ropes and the like, operate in tension and may be exposed to road splash and debris that could damage the mechanical travel limiting devices if not designed to endure those relatively harsh environments. In order to withstand the weight of, and forces acting on, the beams and axle, the links of the chain must be relatively robust which undesirably adds to the overall weight and cost of the heavy-duty vehicle.
The prior art axle/suspension system uses a robust pivot bushing at the pivot connection of a beam to a hanger for the satisfactory management of static loads, roll moments and braking forces that the bushing experiences. The known pivot bushing has specific and differing stiffnesses or resistances to deformation in the vertical and horizontal directions in which forces are applied. The known pivot bushing is designed and constructed to react to vertical, horizontal and lateral forces that are typically encountered during normal operation of the heavy-duty vehicle.
A new and improved positive mechanical down-stop for limiting downward movement of beams and an axle of an axle/suspension system has been developed. The new and improved positive mechanical down-stop limits downward pivotal movement of the beam and axle and creates a force in a direction that the prior art bushing designs did not consider. The new and improved positive mechanical down-stop for the axle/suspension system incorporates a new and improved bushing of the present subject matter.
The axle/suspension system includes a pair of suspension assemblies, each of which is supported by a hanger depending from a frame member of the heavy-duty vehicle. Each suspension assembly includes a beam mounted to the hanger for pivotal movement at a pivot connection. A bumper is fixed to a portion of the beam. The bumper contacts structure to positively limit downward pivotal movement of the beam. A force is created at the pivot connection in a force application direction that is angularly spaced from horizontal and vertical directions.
The pivot connection includes a bushing with an elastomeric bushing body. The elastomeric bushing body has relatively low stiffness or resistance to compressive forces or deformation in a region that is located in a substantially vertical direction. The relatively low stiffness region is located in the elastomeric bushing body angularly spaced from the down-stop force application direction. The bushing has a relatively greater stiffness along the force application direction.
Thus, a need exists for an improved bushing structure for use with a new positive mechanical down-stop of an air spring axle/suspension system to limit downward pivotal movement of the beams and axle. The improved bushing must accommodate the application of non-vertical and non-horizontal forces created by the use of the new positive mechanical down-stop having components under compressive forces to limit downward pivotal movement of the beams and axle.